The invention relates to a process for synthesizing cumene, and more particularly to a zeolite-catalyzed process for synthesizing cumene involving pre-treating benzene and propylene feedstocks to remove catalyst poisons.
Zeolite catalysts, particularly versions of the present generation of catalysts, are very effective for catalyzing industrial-scale cumene synthesis via benzene/propylene reactions. While their catalytic efficacy is impressive, most zeolites are highly susceptible to nitrogen-, sulfur- and oxygen-containing contaminants and olefinic contaminants. These contaminants, also referred to as xe2x80x9cpoisons,xe2x80x9d deactivate the catalyst by blinding (i.e., clogging) the zeolite""s active sites. Since almost all untreated industrial grade benzene and propylenes contain enough poisons to rapidly and significantly degrade the catalytic activity of zeolite catalysts, an effective and low-cost method of stripping the catalyst poisons from the feedstocks would extend the life of the zeolite catalyst and improve the efficiency of zeolite-catalyzed cumene synthesis.
Briefly, the invention relates to a zeolite-catalyzed cumene synthesis process in which benzene and propylene feedstocks are pre-treated to remove catalyst poisons. The benzene feedstock is pre-treated by contact with a xe2x80x9chotxe2x80x9d clay bed, the hot clay bed being at a temperature of about 200 to 500xc2x0 F., preferably about 350 to 500xc2x0 F. and more preferably 350 to 375xc2x0 F., under a pressure sufficient to maintain a substantial portion of the feedstock in a liquid phase. The benzene feedstock is thereafter distilled to separate the benzene from the higher molecular weight materials formed from olefinic poisons during the hot clay treatment. The benzene distillate is also subjected to a xe2x80x9ccoldxe2x80x9d clay treatment wherein the benzene distillate is contacted with an ambient-temperature clay to remove nitrogen-containing catalyst poisons.
The propylene feedstock is pre-treated by contact with an alumina to remove trace sodium compounds and moisture, a molecular sieve to remove moisture, and two modified aluminas to remove catalyst poisons. The pre-treated propylene and benzene feedstocks are then reacted in the presence of a zeolite catalyst to form cumene without causing rapid degradation of the catalyst""s activity.